Disk drives store information on magnetic disks. Typically, the information is stored in concentric tracks on the disk and the tracks are divided into servo sectors that store servo information and data sectors that store user data. A head reads from and writes to the disk. The head may include separate or integrated read and write elements. The head is mounted on an actuator arm that moves the head radially over the disk. Accordingly, the actuator arm allows the head to access different tracks on the disk. The disk is rotated by a spindle motor at a high speed, allowing the head to access different data sectors on the disk.
FIG. 1 illustrates a conventional disk drive 10 that includes a magnetic storage disk 12 that is rotated by a spindle motor 14. The spindle motor 14 is mounted on a base plate 16. The disk drive 10 also includes an actuator arm assembly 18 having a head 20 mounted on a flexure arm 22 which is attached to an actuator arm 24 that rotates about a bearing assembly 26 that is attached to the base plate 16. The actuator arm 24 cooperates with a voice coil motor 28 to move the head 20 relative to the disk 12. The spindle motor 14, the head 20 and the voice coil motor 28 are coupled to electronic circuits 30 mounted on a printed circuit board 32. The electronic circuits 30 include a read channel, a microprocessor-based controller and a random access memory (RAM). Although only a single disk 12 is shown, the disk drive 10 may include multiple disks 12 and therefore multiple corresponding actuator arm assemblies 18.
FIG. 2 illustrates the head 20 flying above the disk 12. The head 20 (which includes a slider and is conventional) is located above the disk surface 42 by a flying height 100. The flying height 100 is created by the interaction between air currents above the disk surface 42 (also known as an air-bearing) caused by rotation of the disk 12 and the aerodynamics of the slider of the head 20.
It is important to maintain the flying height 100. For example, if the head 20 flies too low, it is more likely to contact the disk 12 which could cause stored data to be lost. As another example, if the head 20 flies too low, a particle resting on the disk 12 may attach to the head 20 and change the aerodynamics of the head 20.
FIG. 3 is an air-bearing surface view of the head 20 that illustrates a write portion 110 of the head 20 and a read portion 120 of the head 20. For clarity, the slider of the head 20 is not shown. The write portion 110 includes a write pole 130 and a return 135. The read portion 120 includes a magneto-resistive (MR) read element 140 along with first and second shields 142, 144. The direction of disk rotation is shown by arrow 150 such that the write pole 130 follows the read element 140.
FIG. 4 is a cross-sectional, side view of the head 20 that illustrates a write coil 155, a write gap 160 and a read gap 165. The write portion 110 writes perpendicular magnetic polarity transitions onto the disk 12. Perpendicular recording is well-known in the art and requires a disk that is capable of having perpendicular magnetic polarity transitions recorded thereon, for example, by including a soft magnetic underlayer.
During a write operation, a variable write current is supplied to the write coil 155 to induce magnetic flux across the write gap 160. The direction of the write current defines the direction in which the magnetic flux is oriented across the write gap 160. In simple recording systems, magnetic flux polarized in one direction across the write gap 160 records a binary one while magnetic flux polarized in the opposite direction records a binary zero. In most recording systems, a change in the direction that the magnetic flux travels across the write gap 160 records a binary one while the lack of such change records a binary zero. As the disk 12 travels under the write portion 110, a series of ones and zeros are written to the disk 12.
During a read operation, the first and second shields 142, 144 define the read gap 165 which focuses the magnetic flux for a particular magnetic polarity transition onto the read element 140 by shielding the read element 140 from other sources of magnetic flux. In other words, extraneous magnetic flux is filtered away from the read element 140 by the shields 142, 144. The read element 140 generates a read signal in response to the changing magnetic flux which corresponds to previously recorded data as magnetic polarity transitions in the disk 12 pass underneath it.
The write portion 110 and the read portion 120 are located near the trailing edge of the head 20. Furthermore, the head 20 is pitched relative to the disk 12 such that the trailing edge is closest to the disk 12 (see FIG. 2). Since the write portion 110 trails the read portion 120, the write portion 110 (specifically the write pole 130) is closest to the disk 12. In addition, the write pole 130, the return 135, the read element 140, the first shield 142 and the second shield 144 share a common plane 175 at an air-bearing surface which faces the disk 12.
Disk drives usually store information on disks using longitudinal recording as opposed to perpendicular recording. However, the heads associated with longitudinal recording may be very similar to the head 20 in that the write pole, return, read element, first shield and second shield share a common plane.
When a write current is introduced into the write coil 155, the write portion 110 thermally expands and is brought even closer to the disk 12. This phenomenon is known as pole tip protrusion. Failure to accommodate pole tip protrusion can result in serious consequences, including data loss where the write portion 110 contacts the disk 12.
Accordingly, it would be advantageous to provide a head which reduces pole tip protrusion, while still allowing data to be accurately recorded onto the disk.